I’m sitting in the back seat of a midnight blue Lincoln Continental convertible that looks almost identical to the one that carried John F. Kennedy on November 22, 1963. Two U.S. flags on the hood flutter in the wind as we cruise through downtown Dallas. This meticulously restored 1963 model even features blankets emblazoned with the presidential seal. As we turn left onto Elm Street from Houston Street, my guide, Robin Brown, slows to 14 miles per hour, close to the speed Kennedy’s motorcade traveled along this route. More than sixty years have passed since the assassination, but I still find myself holding my breath as we roll over the first hand-painted X on the pavement marking where the initial shot struck. By the second X,…